The use of oils as herbicide adjuvants is a well established practice in agriculture for improvement of weed control applications through better coverage and penetration of the active ingredient on the leaf surface of the target weed. In many cases, this permits some degree of reduction in the rate of herbicide required, which is particularly desired for synthetic herbicides that are toxic to humans and the environment. Oil-based herbicide adjuvants are often formulated as an herbicidal “emulsifiable concentrate” consisting of a 75-95 wt % hydrocarbon oil or solvent with the balance being emulsifier, and to which the herbicide is added. In use, the herbicidal emulsifiable concentrate is diluted with water to form an oil-in-water emulsion which is then sprayed onto the target area at an appropriate rate.
While most oil-based herbicidal adjuvants have been directed to the control of grassy weeds in crops, little has been done with respect to the use of such adjuvants for the control of broadleaf (dicotyledous) weeds in turfgrass. In one study by McCowan (McCowan, F. H. “Turf Herbicide Rx: Add Oil” April, 1968), it was found that the addition of Sunspray Oil 11E (a mixture of refined paraffin oil and emulsifier at 98:2 wt %, respectively; available from Sunoco, Inc. Philadelphia Pa., USA) to certain herbicides resulted in equal or better weed control in turfgrass when delivered at a rate of 2 gallons of oil per acre. However, the herbicide oil combination also resulted in a significant increase in toxicity to the turfgrass in some cases. Overall, Applicant believes McGowan's findings were not conclusive with respect to the selectivity, effectiveness and phytotoxicity of various herbicide-oil combinations. To the inventor's knowledge, there are currently no high-oil-content herbicide compositions that selectively kill broadleaf weeds on the market for use on turfgrass.
Wide use of selective herbicides like 2,4-D (2,4 dichlorophenoxyacetic acid), Mecoprop (MCPP or methylchlorophenoxypropionic acid) and dicamba (3,6-dichloro-o-anisic acid) for controlling broadleaf weed in turfgrass throughout the world are controversial. The International Agency for Research on Cancer has classified the entire family of phenoxy-type herbicides, and particularly 2-4D, as potentially carcinogenic. Mecopropand dicamba are suspected of being human teratogens. In the interest of public safety, regulatory bodies such as US EPA and Health Canada PMRA have been making label improvements aimed primarily at exposure reduction of 2,4-D and other herbicides to environments.
Control of broadleaf weeds remains a major problem in turfgrass throughout the world. Further, public concerns related to human health and safety as well as the impact on environments resulting from the application of such herbicides, continue to arise. There is, therefore, a need in the art for improved herbicidal compositions for controlling broadleaf weeds in turfgrass that present a reduced risk to humans and to the environment.